Avalanche Forecast

Issued: Jan 31st, 2012 9:11AM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Wind Slabs, Storm Slabs and Cornices.

swerner, Avalanche Canada

South Columbia.

Summary

Confidence

Fair - Freezing levels are uncertain on Friday

Weather Forecast

Tuesday night into Wednesday: Snow amounts 5-10cms, possibly higher amounts in upslope areas. Ridgetop winds switching from the SW to the NW 20-30km/hr. Freezing levels near 700m. Thursday: High pressure building over the province today will bring dry conditions. Freezing levels will remain valley bottom for most of the day, then rising near 700m in the afternoon. Ridgetop winds will blow from the North 30-40km/hr. Friday: Dry conditions. Warm air and rising freezing levels will persist into Saturday. Ridgetop winds switch, and start blowing 15-30km/hr from the SW.

Avalanche Summary

Several reports of natural avalanche activity occurred on Monday up to size 2.5, but the majority were sized 1-2. Explosive testing done on Monday revealed slab avalanches up to size 2, with one report of a 2.5. Most avalanches occurred on N-NE facing slopes above 1900m. There was also a report of natural cornice fall triggering the slope below up to size 1.5. Cornice fall may increase later in the week due to warming temperatures. Remember these observations are region wide, it's important to make your own personal weather, snowpack and avalanche observations that help your decision making process when traveling in your local mountains.

Snowpack Summary

Over the weekend the region received snow amounts near 40-60cms. The initial half of the storm snow came in dryer then the second half, leaving us with upside-down conditions (heavier snow overlying lighter snow). Storm slabs have been forming at all elevations. Wind slabs are developed on lee slopes in the alpine and at treeline from the randy SW winds. Buried below the storm snow seems to be a fairly settled mid-pack, with a couple lingering layers.We continue to monitor the old storm snow which rests on dry cold snow formed during an Arctic Outbreak, and the January 13th surface hoar/facet layer. Recent snowpack field tests have shown generally moderate results, including resistant planar shears. With the warming temperatures I think the snowpack is settling out, and generally bonding. It is possible to see some limited activity from this layer, but I think it may be on its way out. Deep down in the pack the mid December layer has gained a lot of strength and I don't think we'll see any action from this layer until the spring. The average snowpack depth at 1700m is 2-3 m.

Problems

Wind Slabs

Wind slabs 50 - 100 cm in depth are possible as strong winds accompanied the weekend storm. With this much loading I'd give wind exposed terrain a miss as it will need another day to adjust to the new load.

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

Storm Slabs

Up to 60cms of storm snow fell over the weekend forming storm slabs at all elevations. These have been reactive. It may take a few days for the snow to settle out. You're most likely to trigger a storm slab in steep and/or unsupported/convex terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 5

Cornices

Large cornices have formed. You should give them a wide berth whether traveling near them or far below them. Failing cornices have the potential to trigger large avalanches on the slope below.

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Possible

Expected Size

3 - 6

Valid until: Feb 1st, 2012 3:00AM